docs: def advance_recurring_todo(p_todo, p_offset=None, p_strict=False):
      """
      Given a Todo item, return a new instance of a Todo item with the dates
      shifted according to the recurrence rule.
  
      Strict means that the real due date is taken as a offset, not today or a
      future date to determine the offset.
  
      When the todo item has no due date, then the date is used passed by the
      caller (defaulting to today).
  
      When no recurrence tag is present, an exception is raised.
      """
      todo = Todo(p_todo.source())
      pattern = todo.tag_value('rec')
  
      if not pattern:
          raise NoRecurrenceException()
      elif pattern.startswith('+'):
          p_strict = True
          # strip off the +
          pattern = pattern[1:]
  
      if p_strict:
          offset = p_todo.due_date() or p_offset or date.today()
      else:
          offset = p_offset or date.today()
  
      length = todo.length()
      new_due = relative_date_to_date(pattern, offset)
  
      if not new_due:
          raise NoRecurrenceException()
  
      # pylint: disable=E1103
      todo.set_tag(config().tag_due(), new_due.isoformat())
  
      if todo.start_date():
          new_start = new_due - timedelta(length)
          todo.set_tag(config().tag_start(), new_start.isoformat())
  
      todo.set_creation_date(date.today())
  
      return todo